Preclinical Characterization of AZD5305, A Next-Generation, Highly Selective PARP1 Inhibitor and Trapper

Abstract

Purpose: We hypothesized that inhibition and trapping of PARP1 alone would be sufficient to achieve anti-tumor activity. In particular, we aimed to achieve selectivity over PARP2, which has been shown to a play role in the survival of hematopoietic/stem progenitor cells in animal models. We developed AZD5305 with the aim to achieve improved clinical efficacy and wider therapeutic window. This next generation PARPi could provide a paradigm shift in clinical outcomes achieved by first generation PARPi, particularly in combination. Patients and Methods: AZD5305 was tested in vitro for PARylation inhibition, PARP-DNA trapping and antiproliferative abilities. In vivo efficacy was determined in mouse xenograft and PDX models. The potential for hematological toxicity was evaluated in rat models as monotherapy and combination. Results: AZD5305 is a highly potent and selective inhibitor of PARP1 with 500-fold selectivity for PARP1 over PARP2. AZD5305 inhibits growth in cells with deficiencies in DNA repair, with minimal/no effects in other cells. Unlike first generation PARPi, AZD5305 has minimal effects on hematological parameters in a rat pre-clinical model at predicted clinically efficacious exposures. Animal models treated with AZD5305 at doses ≥0.1mg/kg QD achieved greater depth of tumor regression compared to olaparib 100mg/kg QD, and longer duration of response. Conclusions: AZD5305 potently and selectively inhibits PARP1 resulting in excellent antiproliferative activity and unprecedented selectivity for DNA repair deficient versus proficient cells. These data confirm the hypothesis that targeting only PARP1 can retain therapeutic benefits of non-selective PARPi, while reducing potential for hematotoxicity. AZD5305 is currently in Ph1 trials (NCT04644068).

Clinical PARP inhibitors allosterically induce PARP2 retention on DNA

“…binding to PARP2 in cells, which is consistent with the lower hematological toxicity observed in mice for this compound compared to other PARP2 type I clinical inhibitors (37). We have shown recently that reverse allostery can play a role in modulating the ability of a PARPi to kill cancer cells by converting a type III PARPi (veliparib) into a type I inhibitor (UKTT15) (33).…”

“…AZD5305 is a novel PARPi that has been developed as a selective PARP1 inhibitor, in an attempt to decrease the hematological toxicity associated with the clinical PARPi that has been attributed to targeting other PARP family members and in particular PARP2 ( 36, 37 ). AZD5305 was reported to have a 460-fold selectivity for PARP1 over PARP2 with an IC 50 of 0.003 µM in PARP1 compared to 1.4 µM in PARP2 ( 36 ), and a similar selectivity for inhibition of PARP1 over PARP2 in cells ( 37 ).…”

“…AZD5305 is a novel PARPi that has been developed as a selective PARP1 inhibitor, in an attempt to decrease the hematological toxicity associated with the clinical PARPi that has been attributed to targeting other PARP family members and in particular PARP2 ( 36, 37 ). AZD5305 was reported to have a 460-fold selectivity for PARP1 over PARP2 with an IC 50 of 0.003 µM in PARP1 compared to 1.4 µM in PARP2 ( 36 ), and a similar selectivity for inhibition of PARP1 over PARP2 in cells ( 37 ). Aligning the crystal structures of PARP1 CAT bound to an analog of AZD5305 (compound 22, ( 36 )), PARP1 CAT bound to niraparib, and PARP2 CAT bound to olaparib showed that AZD5305 contacts the HD in the middle part of helix F similar to olaparib (Fig.…”

“…We show that a mutation on helix F can partly mimic the effect of some PARPi in our biochemical experiments and in cells. We also tested the new PARP1-selective compound AZD5305 ( 36, 37 ) for reverse allostery in PARP1 and PARP2 and observed that this compound exerts a clear a pro-retention effect on PARP2. Overall, our results indicate that PARPi have drastically different outcomes on DNA retention in PARP1 and PARP2 due to reverse allostery and suggest that some of these effects contribute to PARP2 trapping in cells.…”

Biomarkers beyond BRCA: promising combinatorial treatment strategies in overcoming resistance to PARP inhibitors

“…AZD5305 is known to exert anti-tumor efficacy by inhibition of PARylation, PARP trapping and growth inhibition. Importantly, AZD5305 selectively kills tumor cells with HR deficiency and exhibits limited cytotoxicity in normal cells [ 57 ]. Compared with first-generation FDA-approved PARPi, AZD5305 demonstrates better efficacy, greater target inhibition and improved tolerability [ 56 ].…”